Aprilaire 6908 User manual

NOT CORRECT
ZONE CONTROL SYSTEM
MODEL 6908, 6910, 6912, 6914 AND 6916 BAROMETRIC BYPASS
DAMPER INSTALLATION INSTRUCTIONS
CAUTION: Sharp edges may cause serious injury from cuts. Use care when
cutting and handling ductwork.
1. IDENTIFY BYPASS DAMPER POSITION IN SYSTEM
Identify where the bypass damper is to be installed. The bypass damper must be
located downstream of any heating or cooling components and upstream of all
zone dampers.
The damper may be installed in a horizontal or vertical (upflow) position. It is
recommended that the damper be installed horizontally. The location of the
damper should allow for clearance around the
balancing mechanism for free rotation.
2. INSTALL THE BALANCING
MECHANISM
Install the balancing mechanism collar on
either end of the damper blade shaft and lock
in place with bolt provided. Based on the
damper orientation, move the balancing
mechanism to the position appropriate for the
orientation of discharge (see Figure 1). Lock
into place with the nut provided.
3. INSTALL THE DAMPER TO THE DUCTWORK
Install the damper with crimped end downstream.
For horizontal installation, rotate the damper
such that the damper blade shaft is parallel to
the floor and located above the damper
centerline (see Figure 2).
Secure the damper to the duct with ½” long, #8
or #10 sheet metal screws (not included).
Insulate the damper. Leave clearance for free
rotation of the balancing mechanism.
Figure 1 - Install the Balancing Mechanism
Figure 2 - Horizontal Installation
CORRECT

4. ADJUSTING THE WEIGHTS
A barometric damper maintains a relatively constant pressure drop across itself
until the point that the blade is fully open.
A. Ensure all zone dampers are fully open and that the filter is clean (replace if
necessary).
B. Screw the weights on the balancing mechanism as close to the collar as
possible.
C. Turn on the system blower at high speed. You may need to make a cooling
call to do this. If the outside temperature is below 50°F, do not turn on the
compressor. Disconnect power to the condensing unit by switching off the
circuit breaker or removing the fuse before making a cooling call.
D. Move the weights outward until the barometric damper blade fully closes, then
move the weights out an additional ¼” to ½”.
E. If the damper is installed between the supply and return plenum, then the
pressure drop across the damper is approximately equal to the system
pressure.1
The barometric damper will open and close to try and maintain this pressure
drop when individual zones are calling. The blade will open more when a
smaller zone is calling and less when a larger zone or combination of zones is
calling.
F. To ensure that you are not bypassing too much air2, make a heating or
cooling call (depending on outdoor temperature conditions) from the smallest
zone (i.e. the one with the smallest zone damper). After five (5) minutes,
measure the supply air temperature and ensure it is within normal operating
limits. In the cooling mode, the supply air temperature should be above 40-
45°F. In the heating mode, the air supply temperature should be below about
150°F. Refer to the HVAC equipment manufacturer literature or contact the
equipment manufacturer to find out what the limits are. If the supply air
temperature is not within normal operating limits, move the weight further
down the threaded rod to reduce the bypass air.
©Research Products Corporation 2014
B2203198B
10006029